Airplane landing gear



July l0, 1951 R. w. ALLEN AIRPLANE LANDING GEAR e` sheets-sneet 1original Filed July `v9, 1943 w 1|. ..2 l ...A

July 10, 1951 R. w. ALLEN AIRPLANE LANDING GEAR 6 Sheets-Sheet 2Original Filed July 9, 1943 afan c mamy July 10, 1951 R. w. ALLEN2,560,030

AIRPLANE LANDING GEAR Original Filed July 9, 1943 6 Sheets-Sheet 3Baymonduen July l0, 1951 R. w. ALLEN AIRPLANE LANDING GEAR 6Sheets-Sheet 4 Original Filed July 9, 1943 Wma@ Y Original Filed July 9,1943 6 Sheets-Sheet 5 July 10,1951 R. w. ALLEN 2,560,030

AIRPLANE LANMNG GEAR i u July 10, 1951 R. w. ALLEN 2,560,030

AIRPLANE LANDING GEAR Original Filed July 9, 1945 Patented July 10,i"1951 AIRPLAN E LANDING GEAR Raymond W. Allen, Akron, Ohio, assignor toThe Firestone Tire & Rubber Company, Akron, Ohio, a. corporation of OhioOriginal application July 9, 1943, Serial No.

494,107, now Patent No. 2,459,737, dated January 18,- 1949.

Divided and this application December 22, 1948, Serial No. 66,715

13 Claims.

This invention relates to airplane landing gear, and more especially itrelates to landing gear of the character wherein endless tracks of theso-called caterpillar type are substituted for the pneumatic tirescommonly used with landing gear for aircraft, and this application is adivision of my co-pending application, Serial No. 494,107, led July 9,1943, now Patent No. 2,459,737.

Aircraft landing gear of the type having endless tracks mounted uponpivoted and articulated supporting structures are old and well known inthis art, but those developed heretofore have serious disadvantages andlimitations which the present invention remedies. The landing gear shownherein is highly eilicient and is particularly advantageous for use withvery heavy planes which land at high speeds. It is also superior toprior constructions in that it will permit a heavy, high speed plane toland and take off safely on very rough and uneven terrain. While earlierforms of landing gears have sought to achieve this result, the landinggear shown herein is more eilicient and eiective. It is also betteradapted for use on wet and muddy elds than other forms of landingdevices.

Other objects of the invention are to provide airplane landing gear ofthe caterpillar type capable of taking oi and landing at higher spedsthan heretofore possible and to provide a structure of the charactermentioned capable of absorbing the higher impact forces resulting fromsuch higher speeds.

Another object of the invention is to provide for keeping the endlesstrack taut while the airplane isv running on the ground either inlanding or taxiing.

More specifically the landing gear of the invention aims to provide abogie construction that will support a portion of the load; to providearticulated bogies so that the track will follow the uneven contour ofthe ground; to provide a exible support for the bogies to enableeilicient operation thereof; and to provide means compensating for thelengthening of the track due to tension when a heavy load is applied.Other objects will be manifest as the description proceeds.

Of the accompanying drawings:

Fig. l is a perspective view of a grounded airplane, and landing gearembodying the invention supporting the same;

Fig. 2 is a perspective view, on a larger scale, of landing gear such asshown in Fig. l

Fig. 3 is a section, on a smaller scale, on the line 3 3 of Fig. 4;

Fig. 4 is a side elevation of the track portion of the landing gear,shown in full lines under load on a level surface Fig. 5 is a plan viewof the structure shown in Fig. 4, a portion thereof being in section online e 5 5 of Fig. 4;

Fig. 6 is a side elevation of the landing gear in Fig. 6 as it appearsunder full load on a downwardly inclined surface;

Fig. 8 is a side elevation of the structure shown in Figs. 6 and 7 as itappears when fully loaded and passing over an obstruction on the ground;

Fig. 9 is a side elevation partly in section illustrating the retractedposition of the landing gear; and

Fig. 10 is a sectional detail of the endless band track.

Referring to Fig. 1 of the drawings, there is shown an airplane Ill ofthe bomber type comprising nacelles II. II mounted upon the wingsthereof. Within the nacelles are the motors that drive the propellers I2of the airplane.

landing wheel I3, which wheel is shown in operative or lowered position,the doors I4, I4 of its compartment being open. The tail wheel of thecraft is shown at I5. Within each nacelle II, rearwardly of the motortherein, is a compartment or bay Within which is mounted a retractiblelanding gear that is designated as a unit by the character A and whichis an embodiment of the present invention. The landing units A are shownin the lowered or operative position they assume l when supporting theairplane upon the ground, the` doors I6, which close the compartments ofthe'landing units A when the latter are in retracted or flying position,being shown open. Within each nacelle is a triangular framework Il,shown in broken lines in Figs. 6, 7 and v8, to

which a landing unit A is attached and which may represent a retractiblesupport for the landing gear. but as said framework is not'part of thepresent invention, a more comprehensiveshowing-.-`

thereof is not necessary. Fig. 9 illustrates the landing units inretracted position within nacelle II.

Pivotally connected-at I9 to o ne corner of the triangular framework I'Iis an arm 20 and pivotally connected at 2I to another corner of theframework I1 is a, somewhat longer arm 22.

Near its nose the airplane is provided with a retractible Y The arms 2l,22 have their lower ends pivotally 24 is located intermediate the endsof the arm,

but somewhat nearer the lower end. The arms 2l, 22 and 25 constitute aexible strut or undercarriage structure that carries the track portionof the landing gear, and also carries a shock absorbing element that.absorbs much of the shock incidental to landing of the airplane, and

also prevents rebound thereof. The shock absorbing element,`shown at 25in the drawings, is of conventional telescoping type employing a heavyfluid in the manner of a -dashpot, one end of said element beingpivotally connected to the arms 22 and 25 at the pivot point 24 and theother end of the element being pivotally connected to the arm 25 at 21,intermediate the ends of the later but somewhat nearpivotal connectionI3. The arrangement is such that the arms 23, 22 and 25 assume therelative angular position best shown in Figs. 7 and 8 when theundercarriage is under load, as when the airplane is on the ground, andassume the relative angular positions shown in Fig. 6 when the airplaneis oil the ground with landing gear in extended landing position, theshock absorbing element 25 lbeing so positioned as yieldingly to opposesudden change in the relative positions of said arms.

The track portion of the landing gear or the track unit comprises aframework or frame member consistingr of parallel, spaced-apart, hollow,side rails 30, 30 that are permanently connected to each otherintermediate their ends by a transverse brace or plate 3|. Between thebrace 3i and the rear ends of the side rails 30 the latter carry atransversely extending shaft 32 to which the lower end of the arm 25 ispivotally connected. As is best shown in Fig. 2, the arm 25 is atruss-like structure having two lateral members 25a, 25a, the lower endsof the latter being spaced apart so as to connect with the shaft 32 atopposite end portions thereof, and being positioned beside the innerlateral faces of the respective side rails 30. Preferably the shaft 32is hollow to reduce weight. The track portion of the landing gear isarranged to be carried in determinate angular position with relation tothe arm 25 at times when there is no load on said track portion. Whenthe landing gear is extended preparatory to landing, the track portionwill be somewhat oblique with relation to horizontal, its leading endbeing elevated as compared to its trailing end. 'This position of thetrack portion is shown in Fig. 6. For yieldingly holding the trackportion to the angular position mentioned, the lateral members 25a ofarm 25 are provided, between pivot points 23, 24, with upstandingbrackets 33 that support a hollow transverse bar or shaft 34. The latterprojects from opposite sides of said arm 25, and to each projecting endportion thereof is swivelled the rear end of a cylinder 35. In eachcylinder 35 is a compression spring 35, Fig. 4, and a rod 31 engagedwith said spring and projecting from an apertured closure on the frontend of said cylinder. The outer end of each rod 31 is pivotallyconnected to an anchor bracket 33 secured to a side rail 30 between thepivot point or shaft 32 and the forward end of the rail, which is theright end thereof as shown in Fig. 2 and the left end thereof as shownin Figs. 4 to 8. The structures consisting of the cylinders 35, springs36 and rods 31 support the overbalanced weight of the track unit whichwould otherwise cause the track unit to drop into a vertical position.This device will permit the track unit to swing upwardly about the pivot32 in riding over an obstruction, as shown in Fig. 8, and when the planelands, the load applied to the rear portion of the track will cause thetoggle formed by the lever 25 and the frame 3D to straighten out, thusbringing down the forward end of the track unit, the spring beingfurther compressed during this movement.

Fixedly mounted in the forward extremity of the side rails 30 andsupported at its ends thereby is a hollow axle 40, and Journaledthereon, between said end rails, is a relatively large, hollow wheel ordrum 4I. Fig. 5, are mounted on the axle 40 and retain the drum 4Icentrally of the axle in spaced relation to the side rails 30. Theperiphery of the drum is formed with a plurality of circumferentiallyextending V-shaped grooves adapted frictionally to engage withcomplementally shaped ribs 43, 43, Figs. 5 and i0, formed on the innerface of an endless band track or caterpillar element 44, constitutingthe ground-engaging member of the landing gear. Journaled on the axle 40between the collars 42 and side rails 30 are arms 45, which arms extendobliquely downwardly and rearwardly and have their lower or free endsconnected by a hollow axle 46. A relatively small hollow wheel or drum41 is journaled on the axle 46, the periphery of the drum being formedwith circumferentially extending V-shaped grooves in which the ribs 43of the endless track 44 are receivable. The free ends of the arms 45normally are yieldingly urged rearwardly by tension springs 48, each ofwhich is connected at one end to a xed point on the cross-brace 3l, seeFig. 2, and has its other end connected to a metal clip 49 secured upona projecting end portion of the axle 46, beside arm 45.

A hollow shaft 5I is xedly mounted in the rearward extremity of the siderails 3B, and journaled on said shaft between said side rails andadjacent the latter are arms 52 which extend obliquely downwardly andrearwardly, substantially in parallelism with the arms 45, and havetheir lower, free ends connected by a hollow axle 53. Journaled upon theaxle 53 between arms 52 is a hollow wheel or drum 54 of substantiallythe same diameter as the drum 4I at the front end of the landing gear,the periphery of said drum being formed with V-shaped grooves in whichthe ribs 43 of the endless track 44 are receivable. As shown in Fig. 5,the drum 54 is provided interiorly at one end with a brake of theconventional fluid pressure operated friction disc type. The hub and rimportion of the drum are connected by an annular structure 55 thatcarries one set of brake-discs, the other set being carried by anannular fixture 56 that is bolted to a flange 51 formed on the arm 52.Pressure fluid for actuating the brake is connected to the latter by aflexible conduit 58 that connects with a suitable port formed in saidfixture 456. Obviously a similar brake could be provided at the otherend of the drum, which brake would be connected in parallel with thefluid supply conduit 58. When the landing gear is applied to aircraftcarrying heavier loads, the forward drum 4i also may be equipped withbraking means.

Positioned between the drum 41 and the drum Collars, such as the collar42,

54 is a bogie comprising a lat top plate 60 and end plates 6l, 6| thatare of trapezoidal shape, the top plate being secured to the shorter ofthe parallel sides of the end plates. The end plates 6I carry two hollowaxles 62, 62, and journaled on said axles are hollow wheels or drums 63.The bogie wheels 63 are identical with each other and preferably areidentical with the drum 41. Theperiphery of each wheel 63 is also formedwith the V-shaped grooves for the endless track 44. Journaled inbearings in each end plate 6I is a shaft 64, the ends of which projectlaterally beyond said end plates. Pivotally connected to each of theprojecting end portions of shaft 64 are two links 65 and 66, which linksextend forwardly and rearwardly, respectively, both of the links oneither side of Ithe structure being disposed in the same vertical plane.The rear end of each of the rearwardly extending links 66 is pivotallyconnected to a projecting end portion of the rear axle 53 of thestructure, and the front ends of the links 65 are pivotally connected ata midway point to the arms 45 by the shaft 61. The arrangement is suchthat the links 65, 66 maintain the bogie in proper relative position ina fore and aft direction, yet enable the bogie to rise or fallrelatively of the cross-brace 3|, 'and to tilt angularly about the shaft64 for a purpose presently to be explained. It will be observed that thelinks 65 and 56 extend somewhat upwardly from the-shaft 64 to shaft 61and axle 53, and are at an angle to each other so as to act as a toggleagainst the arms 45 and 52 when the bogie is moved up or down withrelation to the side rails 30.

The bogie is disposed directly below the crossbrace 3|, and positionedbetween the latter and the top plate 60 of the bogie and secured to eachof them is a pneumatic spring element comprising a bellows-shapedstructure 10. The structure 10 is centrally disposed with relation tothe sides of the landing gear and is composed of flexible, imperviousmaterial. It is preferably formed with a medial circumferential reducedor constricted region, which region is encircled by an inextensiblemetal girdle ring 1|. Valve 12 is provided for inflatin'g the bellowsstructure with compressible fluid such as air, the air within thebellows being maintained at sufficient pressure to enable the bogie tosupport its proper proportionate share of the load on the landing gear.The arrangement provides ready means by which the landing gear may beadjusted to support loads of various weights. Furthermore, the inflatedbellows urges the bogie toward the lower reach of the endless track 44and maintains the latter taut when there is no load on the landing gear.

During flight each landing unit A is carried y Within closed nacelle Il'of the airplane 10, but preparatory to landing is lowered to theposition shown in Fig. 6. It will be observed that the shock-absorbingelement 26 is in extended condition and holds the undercarriagestructure consisting of the arms 20, 22 and 25 in somewhat openposition. Furthermore, the compression springs in the cylinders 35 holdthe entire track portion of the landing gear in somewhat tilted positionso that the lower or ground-engaging reach of the endless track 44 isinclined upwardly with relation to the horizontal, toward the forward orleading end of the landing gear. Thus in landing upon level ground,contact is first made near the rear drum 54 of the gear, and thenprogressively forwardly toward the drum 41 as more load is applied tothe gear, the arrangement being such that the probability of nosingover, due to the striking of small obstructions, is reduced. In Fig. 4the position of the track structure in loaded position on level groundis shown in full lines, the relative positions of the various elementsin unloaded condition, as in flight, being indicated in broken lines.

The major portion of landing impact is absorbed in the shock absorber 26as the arms 20 22 and 25 move from the positions shown in Fig. 6 to thepositions such as shown in Fig. 7 or 8. A minor, but appreciable portionof the impact is absorbed in the track portion of the landing gear,especially by the endless band track itself. It will be apparent thatthe impact of landing will result in the swinging of the arms 45 and 52rearwardly. 'lhis would result in a slackening in the normal tension inthe endless track 44 were it not for the action of the bogie. Impactwith the ground causes the side rails 30 to move downwardly relativelyof the bogie with the result that the links 65, 66 connected thereto actas toggles to force the free ends of the arms 45 and 52 away from eachother, with the result that greater than normal tension is imparted tothe endless track, which tension supplements the force absorbed by thedeforming of the pneumatic cush- .ion 10 in cushioning the landingimpact.

The feature of automatically imparting additional tension to the endlesstrack upon landing also is advantageous `in that it counteractscentrifugal force in the track as it is driven rapidly over the ground.It is also advantageous in keeping the track in tight frictionalengagement with the drums 4| and 54 so that braking force applied to thelatteriwill be efciently transmitted to the track.

Since the weight of the airplane is applied to the side rails 30 of thelanding gear at 32, forwardly of the rear axle 53, the nose or leadingend of the gear moves downwardly against the force of the springs incylinders 35, so that the lower reach of the track is in Contact withthe ground over a large area. The action is shown in Fig. 4, where thefreely suspended position of the track unit is shown in dotted lines andthe loaded position in full lines.

The arrangement by which the bogie may swivel or tilt about the shaft 64is especially advantageous when moving over rough ground, as shown inFig. 8, since it enables both bogie wheels to maintain normal engagementwith the endless track and prevents undue slackening of the ten` sion inthe latter. Moreover, the use of a deformable pneumatic spring membersuch as the bellows 10 enables substantially maximum downward pressureto be exerted on the bogie at all times, notwithstanding the variousangular positions the latter may assume. The forward roller 41 willyield in going over obstructions, its upward movement being resisted .bythe cushion 10 through the toggle mechanism. The spring 48 acts as abalance for the cushion 10. The drum 54 also has the ability to yield,through the cushion 10. As the several rollers 41, 63 and 54 haveconsiderable freedom of movement, the device will accommodate itself toall manner of rough and uneven ground.

The track 44 as illustrated in detail in Fig. 10 has a thin, flexible,molded rubber body structure 13, a frictional inner facing of rubberizedfabric 14, a tread 15 of tough, abrasion-resistant rubber compound, anda reinforcing structure of flexible stranded steel wires 16 embedded inthe gum plies 11, the whole being vulcanized in annular form as anintegral body. The wires are small iiexible cables placed closelytogether. These cables. which are spaced approximately 14 to the inch,are made up of a plurality of strands of very ine wire, the completecable being approximately .030" in diameter. The cables which have beenfound to give the best results are made of what is known as ilne tirewire with the specifications as 'U3/.0058. As a result the wirereinforcement is very flexible so that it will not cut through the belt.A belt so constructed will withstand the high speeds to which the trackis subjected on landing.

Because the endless tracks M having a much greater area of contact withthe ground than have the pneumatic tires such as usually are employed onlanding gear, it follows that the braking effort of the presentinvention will have greater mechanical advantage than braking applied towheels equipped with pnumatic tires. Thus, airplanes equipped with theimproved landing gear of the invention may land at higher speeds thanairplanes not so equipped, or they may land on elds provided withshorter runways.

The shaft 32, where the caterpillar track unit is pivotally connected tothe undercarriage structure, is disposed rearwardly of the center ofgravity of the track unit and the ground-contacting area of the track,with the result that the possibility of nosing over upon landing isfurther reduced.

It will also be noted that the arrangement is such that the track andits reticulated supporting structure will conform to the surface of theterrain more eiectively and safely than previous landing gears of thisgeneral type. Thus. in Fig. 7 is shown the position which the track unitassumes when the ground slopes downwardly and forwardly. while Fig. 8shows the position which is assumed on an upwardly sloping terrain or ingoing over obstructions. The fact that the forward drum 4l is elevatedabove the contact area of the track enables the device to climb overobstacles. The superior flexibility of the structure which absorbs theirregularities of all types of rough ground greatly reduces any tendencyof the plane to upset or nose over during landing or taking off on veryrough and uneven ground. This is all accomplished without danger of thestructure throwing its landing track, as is often the case with previouslanding gears of this type.

It will be understood that the means shown for -spreading the main trackcarrying drums may be altered, it being possible to employ other meansresponsive to the load for spreading the drums under load or to take upany loosening of the belt by centrifugal force while under load. y

While the specifications of the wire reinforcement given above have beenfound to be highly satisfactory and eillcient, it will be understoodthat these details may be modied, it being essential to maintain a veryflexible construction which will, however. have the requisite strength.It will also be noted that by the provision of a plurality of ribs ofequal size and spacing, the belt may shift on the rolls and pulleys to aconsiderable extent without actual loss of the belt as any rib will seatproperly within any groove and the belt-still be serviceable.

Other modifications may be resorted to without departing from the spiritof the invention or the scope thereof as defined by the appended claims.

What is claimed is:

1. A track-laying landing gear for aircraft.

comprising a rigid frame. a rst roller ,iournaled on said frame, a firstpair of arms pivoted on said frame. on an axis spaced from the axis ofsaid roller. journal means on said frame intermediate the axis ofpivoting of said arms and the axis of said roller, for pivotal mountingof gear-retract- 1118 mechanism of an aircraft. a second roller mountedfor rotation between said pair of arms on an axis spaced from the axisof pivoting of said arms, a second pair o! arms pivoted on said frame onthe opposite side of the said journal means from said first pair ofarms, a third roller mounted for rotation between said second pair ofarms on an axis spaced from the axis of pivoting thereof, toggle meansinterconnecting said rst pair of arms with said second pair of arms, anda resilient connection between said frame and an intermediate part ofsaid toggle means and oifset from said journal means.

2. A track-laying landing gear for aircraft, comprising a rigid frame,track rollers mounted for rotation on a pair of lever systems pivoted onspaced axes on said frame. journal means on lsaid frame, intermediatesaid axes. for pivotal mounting of the gear-retracting mechanism of anaircraft. another track roller journaled on said frame in spacedrelation to said journal means,

toggle means interconnecting said lever systems, and resilient meansLinterconnecting said frame and an intermediate part of said togglemeans.

3. A track-laying landing gear for aircraft, comprising a rigid frame.track rollers mounted for rotation on a pair of lever systems pivoted onspaced axes on said frame, journal means on said frame, intermediatesaid axes, for pivotal mounting of the gear-retracting mechanism of anaircraft,janother track roller journaled on said frame in spacedrelation to said journal means, toggle means interconnecting said leversystems. and resilient means interconnecting said frame and anintermediate part of said toggle means,

said resilient means including a bogie pivoted on said toggle means andmounting a pair of track rollers. y

4. A track-laying landing gear for aircraft. comprising a rigid frame,track rollers mounted for rotation on a pair of lever systems pivoted onspaced axes on said frame, journal means on said frame, intermediatesaid axes, for pivotal mounting of the gear-retracting mechanism of anaircraft, another track roller journaled on said frame in spacedrelation to said journal means. toggle means interconnecting said leversystems. and resilient means interconnecting said frame and anintermediate part of said toggle means. said resilient means including afluid-containing bellows and a bogie pivoted on said toggle means andmounting a pair of track rollers.

5. A track-laying landing gear for aircraft, comprising a rigid frame,track rollers mounted for rotation on a pair of lever systems pivoted onspaced axes on said frame, journal means on said frame, intermediatesaid axes, for pivotal mounting of the gear-retracting mechanism of anaircraft, another track roller journaled on said frame in spacedrelation' to said journal means, toggle means interconnecting said leversystems and attached to one of said lever systems between its mountedroller and the said frame, and resilient means interconnecting saidframe and an intermediate part of said toggle means.

6. A track-laying landing gear for aircraft, comprising a rigid frame,track rollers mounted for rotation on a pair of lever systems pivoted onspaced axes on said frame, journal means on said frame, intermediatesaid axes, for pivotal mounting of the gear-retracting mechanism of anaircraft, another track roller journaled on said frame in spacedrelation to said journal means, toggle means interconnecting said leversystems and being attached to an intermediate part of that one of thesaid lever systems lying on the same side of the said journal means asthe lastmentioned track roller, and resilient means interconnecting saidtrame and an intermediate part of said toggle means.

7. A track-laying landing gear for aircraft, comprising a rigid frame,track rollers mounted for rotation on a pair of lever systems pivoted ouspaced axes on said frame, journal means on said framejintermediate saidaxes, for pivotal mounting of the gear-retracting mechanism of anaircraft, another track roller journaled on said frame co-axially withthe pivot axis of one of said lever systems, toggle meansinterconnecting said lever systems, and resilient means interconnectingsaid frame and an intermediate part of said toggle means.

8. In a device as in claim 5, resilient means urging said one of saidlever systems toward the said frame, in opposition to thefirst-mentioned resilient means.

9. A track-laying landing gear for aircraft, comprising a rigid frame,track rollers mounted for rotation on a pair of lever systems pivoted onspaced axes on said frame, journal means on said frame, intermediatesaid axes, for pivotal mounting of the gear-retracting mechanism of anaircraft, another track roller journaled on said frame in spacedrelation to said journal means, toggle means interconnecting said leversystems and attached to one of said lever systems 'between its mountedroller and the said frame and to the other of said lever systems,co-axially with its mounted roller, and resilient means interconnecting.said frame and an intermediate part of said toggle means.

10. A track-laying landing gear for aircraft comprising a rigid frame,track rollers mounted 4 for rotation on arms pivoted on axes spacedalong said frame, journal means on said frame, intermediate said axesand adjacent one of said arms, for pivotal mounting of thegear-retracting mechanism of an aircraft, a track roller journaled onsaid frame for rotation about one of said axes, a toggle mechanismarticulated to one of said arms co-axially with the roller mountedthereon and to the other of said arms intermediate the roller mountedthereon and its .axisof pivoting, resilient means attached to the frameand to an intermediate part of said toggle linkage, said resilient meanscomprising a spring, and a bogie pivoted on said toggle mechanism a pairof track rollers.

11. A device as in claim 10, said resilient means being so positionedthat the said arms at all times form acute angles with the lineadjoining their pivot axes.

12. A device as in cla-im 10, said resilient means being so positionedthat the said arms at al1 times form acute angles with the line axes,the arm pivoted co-axially with a track roller being directed generallytoward said journal means, and the other arm being directed generallyaway from said journal means.

13. A device as in claim 10, spring means connecting said other of saidarms to said frame and acting in opposition to said resilient means.

RAYMOND w. ALLEN.

REFERENCES CITED UNITED STATES PA'I'ENTS Number ate Name 1,480,078Kegresse Jan. 8, 1924 1,831,012 Kornbeck Nov. 10, 1931 2,041,599Fergusson May 19, 1936 2,281,351 Dowty Apr. 28, 1942 2,416,183 KraftFeb. 18, 1947 FOREIGN PATENTS Number Country Date 432,868 Great BritainOct. 30, 1933 571,024 Great Britain Aug. 2, 1945 OTHER REFERENCES"Flight, magazine for September 30, 1943. Richmond (Va.) Times-Dispatchfor July 24, 1943.

and carryingjoining their pivot

